Question: $\dfrac{7}{8} - \dfrac{2}{5} = {?}$
Answer: $ = {\dfrac{7 \times 5}{8 \times 5}} - {\dfrac{2 \times 8}{5 \times 8}} $ $ = {\dfrac{35}{40}} - {\dfrac{16}{40}} $ $ = \dfrac{{35} - {16}}{40} $ $ = \dfrac{19}{40}$